Cross-stage neural pattern similarity in the hippocampus predicts false memory derived from post-event inaccurate information

The misinformation effect occurs when people’s memory of an event is altered by subsequent inaccurate information. No study has systematically tested theories about the dynamics of human hippocampal representations during the three stages of misinformation-induced false memory. This study replicates behavioral results of the misinformation effect, and investigates the cross-stage pattern similarity in the hippocampus and cortex using functional magnetic resonance imaging. Results show item-specific hippocampal pattern similarity between original-event and post-event stages. During the memory-test stage, hippocampal representations of original information are weakened for true memory, whereas hippocampal representations of misinformation compete with original information to create false memory. When false memory occurs, this conflict is resolved by the lateral prefrontal cortex. Individuals’ memory traces of post-event information in the hippocampus predict false memory, whereas original information in the lateral parietal cortex predicts true memory. These findings support the multiple-trace model, and emphasize the reconstructive nature of human memory.


Supplementary Figure 1. Materials of eight original events.
For each of eight events, 50 images were used to describe one theme, including 12 critical items (colored in red) and 12 control items (colored in green) that would be tested later. To increase the credibility of narratives, critical and control items would not be set to the first two slides of each event, and any two of critical items from each event would not appear one after the other (i.e., they would be interspersed with generic and control items). To obtain a balanced design, two versions of critical items were developed and counterbalanced across participants. For example, in the misinformation group, one participant saw an image depicted that a man took a blue candy box, and later would read the misinformation of a red candy box; whereas another participant saw an alternative image depicted that a man took a red candy box, and later would read the misinformation of a blue candy box. Images of people in the figure are blurred according to journal's regulations, while images in the experiment were displayed in high resolution. Permission has been obtained from these individuals to depict them in this figure. during the original-event stage (image 26), and then read the misinformation "the man took a red candy box" during the post-event stage (narrative 26). If this participant retrieved the original information (i.e., blue candy box) while reading the misinformation, then this participant was more likely to produce a true memory than a false memory in the subsequent memory test. In this case, the cross-stage neural pattern similarity between the original-event and post-event stages was caused by the overlap between the encoding of the original information during the original-event stage (i.e., the man took a blue candy box) and the retrieval of the original information during the post-event stage (i.e., the man took a blue candy box).

Supplementary Figure 6. Brain regions showing differences between true and false memories in item-specific neural pattern similarity for OP (between original-event and post-event stages), OM (between original-event and memory-test stages), and PM (between post-event and memory-test stages) in
Exp. 2 (thresholded at Z > 2.3). Multiple brain regions showed greater item-specific neural pattern similarity between the original-event and post-event stages for true memory than false memory, whereas no brain region showed the reversed pattern.
These results suggest that the cross-stage neural pattern similarity between the original-event and post-event stages is mainly due to the retrieval of original information during the post-event stage, rather than due to the blurring of the two pieces of encoded information. showed greater item-specific representations of information during the post-event and memory-test stages (i.e., OP, OM, and PM) for true memory than that for correct control. However, only the right superior parietal lobe showed greater item-specific representations of original information during the post-event stage (i.e., OP) for correct control than that for true memory.

Supplementary Figure 8. Brain regions showing differences between correct control and incorrect control in item-specific neural pattern similarity for OP (between original-event and post-event stages), OM (between original-event and memory-test stages), and PM (between post-event and memory-test stages), respectively in Exp. 2 (thresholded at Z > 2.3).
For each control item, its post-event narrative (e.g., reading "the lady was walking down the street, and there was a soda can next to her feet") was consistent with the corresponding original image (e.g., seeing "the lady was walking down the street, and there was a soda can next to her feet"). Thus, the contrast between correct and incorrect control reflects memory representations of consistent information. Several cortical regions (e.g., the bilateral superior parietal lobe and left middle temporal gyrus) showed greater itemspecific representations for correct control compared to incorrect control. No region showed the reversed pattern.

Supplementary Figure 9. Brain regions showing univariate activation differences between true and false memories during the original-event, postevent, and memory-test stages in Exp. 2 (thresholded at Z > 2.3).
Left: During the original-event stage, the bilateral frontal and visual cortex showed greater activations for subsequent true memory compared to false memory; whereas the precuneus and cingulate gyrus showed greater activations for subsequent false memory compared to true memory. These results suggested that, during the originalevent stage, greater attention to visual details may support subsequent true memory than false memory 1 , whereas greater attention to gist processing of the original events may support subsequent false memory than true memory. Middle: During the post-event stage, the bilateral frontal, parietal, and middle temporal cortex, as well as medial frontal cortex and cingulate gyrus showed greater activations for subsequent true memory compared to false memory; whereas bilateral superior temporal cortex showed greater activations for subsequent false memory compared to true memory. These results suggested that, during the postevent stage, a greater prefrontal monitoring might support subsequent true memory than false memory 2,3 , whereas a greater language processing might support false memory than true memory. Right: During the memory-test stage, the bilateral frontal, parietal, and middle temporal cortex, as well as medial frontal cortex and cingulate gyrus showed greater activations of true memory compared to false memory; but no brain region showed greater activations of false memory compared to true memory. NA: not applicable. Those brain regions were located within the core recollection network, suggesting that true memory was associated with recovering more information than false memory during the memory-test stage 4 .

Supplementary Figure 10. Brain regions showing univariate activation differences between true memory and correct control during the originalevent, post-event, and memory-test stages in Exp. 2 (thresholded at Z > 2.3).
Left: During the original-event stage, the bilateral prefrontal cortex, parietal lobe, middle temporal gyrus, fusiform gyrus, and lateral occipital cortex showed greater activations for subsequent true memory compared to correct control; whereas the intracalcarine cortex, lingual gyrus, and occipital pole showed greater activations for subsequent correct control compared to true memory. These results suggested that, during the original-event stage, greater attention to high-level visual details (using the lateral visual cortex) might support subsequent true memory than correct control, whereas greater attention to low-level visual details (using the medial visual cortex) might support subsequent correct control than true memory. Middle: During the post-event stage, the bilateral prefrontal cortex, paracingulate gyrus, inferior parietal lobe and middle temporal gyrus showed greater activations for subsequent true memory compared to correct control; whereas bilateral postcentral gyrus, superior temporal gyrus, and precuneus showed greater activations for subsequent correct control compared to true memory. Similar to the results from the contrast between true and false memories, the results from the contrast between true memory and correct control suggested that, during the post-event stage, a greater prefrontal monitoring might support subsequent true memory than correct control, whereas a greater language processing might support correct control than true memory. Right: During the memory-test stage, the bilateral prefrontal cortex, inferior parietal lobe, middle temporal gyrus, and medial prefrontal cortex showed greater activations for true memory compared to correct control; whereas precuneus and bilateral superior temporal gyrus showed greater activations for correct control compared to true memory. It suggested that true memory was associated with recovering more visual information than correct control, while correct control was associated with recovering more semantic information than true memory during the memory-test stage.

Supplementary Figure 11. Brain regions showing univariate activation differences between correct control and incorrect control during the originalevent, post-event, and memory-test stages (thresholded at Z > 2.3).
Left: During the original-event stage, the bilateral visual cortex showed greater activations for subsequent correct control compared to incorrect control; whereas the bilateral cingulate gyrus showed greater activations for subsequent incorrect control compared to correct control. These results suggested that, during the original-event stage, greater attention to visual details might support subsequent correct control than incorrect control, whereas greater attention to gist processing might lead to subsequent incorrect control than correct control. Middle: During the post-event stage, the bilateral middle frontal and left temporal gyrus showed greater activations for subsequent correct control compared to incorrect control; whereas the bilateral superior and medial frontal cortex, bilateral inferior parietal lobe, precuneus, and lingual gyrus showed greater activations for subsequent incorrect control compared to correct control. They might reflect the neural repetition enhancement and suppression during the post-event stage. Right: During the memory-test stage, the medial prefrontal cortex, posterior cingulate gyrus, and bilateral inferior parietal lobe showed greater activations of correct control compared to incorrect control; whereas the bilateral superior frontal gyrus showed greater activations of incorrect control compared to correct control. It suggested that correct control was associated with recovering more information than incorrect control, while incorrect control was associated with more verification processes than correct control during the memory-test stage. Note. Due to the key role of the hippocampus in memory, prior studies have reported results of hippocampal univariate activations using fMRI data during one or two of three memory stages. However, their findings were mixed. It might be due to differences in their experimental design (e.g., stimulus duration, sensory modality, and interval). , which may be caused by the design problem of the experimental material of foils. For critical items, the options of original information (e.g., a blue candy box) and misinformation (e.g., a red candy box) were counterbalanced across participants, but not for the foil option (e.g., a white candy box). Moreover, the reason that participants were less likely to select the foil option may be that they perceived the original and misinformation options were more reasonable than the foil option (e.g., red or blue candy boxes are more common than white candy boxes in real life). This did not affect the main results of the current study, because we examined the behavioral performance of misinformation effect by measuring the difference between false memory and the endorsement rate of foils rather than measuring false memory alone. Besides, true memory was higher than correct control in the neutral group (t (41)   In addition, we examined the memory effect for control items by comparing correct control and incorrect control on item-specific hippocampal pattern similarity in OM or in PM. For OM, the effect of item specificity for correct control was higher than for (2) Additional results using partial correlations for PM and OM:

Supplementary
Partial correlations were calculated for PM and OM at the trial level for corresponding and non-corresponding items, separately. For the corresponding items, a partial correlation for PM was calculated between the neural pattern of one item during the memory-test stage (e.g., test item 26) and the neural pattern of its corresponding narrative during the post-event stage (e.g., narrative 26), after controlling for the neural pattern of its corresponding image during the original-test stage (e.g., image 26). For the non-corresponding items in the same event, partial correlations for PM were calculated between neural patterns during the memory-test (e.g., test item 26) and post-event stages (e.g., narrative 1), after controlling for that during the original-test stage (e.g., image 1). Then, these similarity scores were transformed into Fisher's Z scores, which were then averaged to generate the neural pattern similarity value for each type of trial. The same method was used to calculate partial correlations for OM, except that neural pattern similarities were computed between original-event and memory-test stages after controlling for the neural pattern during the post-event stage. It should be noted that we did not calculate partial correlations for OP, because the memory test was conducted after the original and post-event stages (i.e., OP was unlikely to be influenced by neural patterns during the subsequent memory test). Using the partial correlations for PM and OM and original correlations for OP, we conducted the 3 by 4 by 2 repeated measures ANOVA on the hippocampal pattern similarity.
These additional analyses confirmed the significant results as reported in Fig. 3d  Using the method of Meng, et al. 8 , we reported p values after correction for comparing correlated correlation coefficients. We used the cocor package (version 1.1-4), which is a software package for the R programming language 9 . The results after correction were virtually the same as those reported in the main text (i.e., before correction).

Methods in detail:
( Finally, in order to test the contrast of OP vs. OM (for item-specific representation), the paired t-test was used to compare Meng' s z scores for OP vs. OM (for corresponding items) and for OP vs. OM (for non-corresponding items in the same event).
(2) OM vs. PM for item-specific representation The same method was used as described above, except that comparisons between OM and PM were controlled for OP.
(3) OP vs. PM for item-specific representation The same method was used as described above, except that comparisons between OP and PM were controlled for OM.
Supplementary 0.0002 ± 0.0836 0.0036 ± 0.0823 0.0041 ± 0.0824 -0.0003 ± 0.0818 non-corresponding 0.0014 ± 0.0317 0.0015 ± 0.0309 0.0009 ± 0.0309 0.0016 ± 0.0310 item-specific -0.0012 ± 0.0792 0.0021 ± 0.0774 0.0032 ± 0.0777 -0.0019 ± 0.0768 PM corresponding -0.0030 ± 0.0835 0.0008 ± 0.0817 0.0031 ± 0.0823 0.0022 ± 0.0818 non-corresponding -0.0010 ± 0.0308 -0.0005 ± 0.0310 -0.0012 ± 0.0307 0.0005 ± 0.0306 item-specific -0.0020 ± 0.0786 0.0013 ± 0.0767 0.0043 ± 0.0783 0.0017 ± 0.0779 Note. OP: Neural pattern similarity between original-event and post-event stages. OM: Neural pattern similarity between original-event and memory-test stages. PM: Neural pattern similarity between post-event and memory-test stages. Bolded scores represent item-specific neural pattern similarity, which was calculated by the neural pattern similarity for corresponding items minus that for non-corresponding items in the same event for each type of memory. True: true memory of critical items. False: false memory of critical items. Correct: correct control items. Incorrect: incorrect control items. For each participant, the whole hippocampus was divided into its anterior and posterior segments based on the location of uncal apex in the native space. However, this three-way interaction was not significant for true memory, false memory, or incorrect control (ps > 0.064). To further interpret this three-way interaction for correct control, we examined the data by stage pair. There was a significant two-way interaction between item specificity and ROI in OP (F(1, 56) Table 9. The means and standard deviations (Mean ± SD) for the Fisher's Z scores of within-participant and between-participant correlations between hippocampal item-specific representation and behavioral performance of false memory, correct control, or true memory in Exp. 2.
Note. OM: Neural pattern similarity between original-event and memory-test stages.
PM: Neural pattern similarity between post-event and memory-test stages.
Item-specific neural pattern similarity was calculated by the neural pattern similarity for the corresponding items minus that for the non-corresponding items in the same event for each memory type. Greater within-participant than between-participant neural-behavioral correlations are shown in bold. Lower within-participant than between-participant neural-behavioral correlations are shown in italics. As shown by a previous study 10 , the results of individuation analysis are meaningful only when the within-participant correlation is greater than the between-participant correlation. The negative within-participant correlation for true memory contradicts the premise of the individuation analysis. Therefore, we are not concerned with this negative correlation.